Tip shroud for moving blades of gas turbine

ABSTRACT

A tip shroud (11) for a moving blade to be used at a downstream stage of a gas turbine. The tip shroud is extended in its creep lifetime by feeding it effectively with cooling air. In the tip shroud (11), there are cut-off portions (12, 13) which are passed by a hot combustion gas so that they are influenced by thermal stress. On the shroud faces, there are formed grooves (31, 32; 33, 34), and cooling guide covers (21, 22) are mounted in the grooves. The cooling guide covers (21, 22) are closed at one side with members (21a, 22a) and open at an end thereof. The covers function to cover the air holes (17) so that the cooling air is fed to the cut-off portions (12, 13) individually. The metal temperature rise at the cut-off portions (12, 13), as will be influenced by the hot combustion gas, can be suppressed so as to extend the creep lifetime of the tip shroud.

TECHNICAL FIELD

The present invention relates to a tip shroud for a gas turbine movingblade and, more particularly, to a tip shroud for a moving blade, whichis used at a downstream stage and is made thin and light to havemulti-holes therein for cooling purposes, and which is extended in itscreep lifetime by cooling it effectively.

DESCRIPTION OF RELATED ART

FIGS. 8(a)-8(b) show one example of a prior art moving blade to be usedat a downstream stage of the gas turbine. FIG. 8(a) is a longitudinalsection, and FIG. 8(b) is a section taken in the direction of arrowsD--D of FIG. 8(a). In order to enhance the effect of cooling the gasturbine, which in recent years is subject to hotter and hottertemperatures, there has been adopted a system in which a moving blade tobe used at a downstream stage is made thin and light but long and inwhich multiple holes are formed to feed cooling air to cool the insideof the moving blade. FIG. 8 shows one example of the moving blade, inwhich reference numeral 60 designates a moving blade, numeral 61 a bladeroot, and numeral 62 a hub having an internal cavity 64 extending alonga hub portion 63 by 25% of the total blade length and supported by coresupporting ribs 65. Numeral 66 designates a plurality of holes orpassages which are formed from the upper portion of the hub portion 63to a blade end 67, as shown in FIG. 8(b). A tip shroud 68 is mounted onthe leading end of the moving blade 60, and includes air holes forguiding the cooling air from the holes 66 so as to release the coolingair 70 to the outside.

In the moving blade 60 thus constructed, the cooling air 70 is guidedfrom the blade root 61 into the cavity 64 to cool the cavity 64 and thenflows through the holes 66 and the blade end 67 to cool the blade sothat the cooling air is released, while cooling the tip shroud 68, fromthe air holes formed in the tip shroud 68 to a combustion gas passage.

FIGS. 7(a)-7(b) show another example of a gas turbine moving blade,which is used at the downstream stage of the gas turbine as in theexample of FIG. 8. FIG. 7(a) is a longitudinal section, and FIG. 7(b) isa section taken in the direction of arrows C--C of FIG. 7(a). In FIG. 7,reference numeral 50 designates a moving blade, numeral 51 a blade root,and numeral 52 a hub having an internal cavity 54 extending along a hubportion 53 by 25% of the total-blade length and supported by coresupporting ribs 55. Numeral 56 designates a plurality of holes orpassages which are formed from the upper portion of the hub portion 53to a blade end 57. A tip shroud 58 is mounted on the leading end of themoving blade 50. These structures are identical to those of the exampleshown in FIG. 8. In the example of FIG. 7, however, a number of pin fins59 are provided in the cavity 54 by projecting them from the two innerwall faces or by connecting them to the two inner wall faces.

In the moving blade 50 thus constructed, the cooling air 70 flows fromthe blade root 51 into the cavity 54, and its flow is disturbed by thepin fins 59 to enhance the thermal conductivity and accordingly thecooling efficiency of the internal cooling air in the hub portion 53.After this, the cooling air 70 flows through the holes 56 to the bladeend 57 to cool the blade 50 and the tip shroud 58. The cooling air isreleased from the air holes formed in the tip shroud 58 to thecombustion gas passage.

As described hereinbefore, the moving blade to be used at the downstreamstage of the gas turbine is made light and long, and its tip shroud isshaped so as to be exposed to the hot gas so that it is liable to crack.FIGS. 6(a)-6(b) show the moving blade and the tip shroud. FIG. 6(a) is aside elevation, and FIG. (b) is a top plan view of the tip shroud. Onthe leading end of a moving blade 10, as shown in FIG. 6(a), there ismounted a tip shroud 11, which is provided with flanges 14 and at itstwo end portions and a flange 16 at its central portion. However, thetip shroud 11 has portions at its circumferential end portions that areliable to have a concentrated thermal stress.

FIG. 6(b) is a top plan view of the aforementioned tip shroud. At thetwo circumferential sides of the tip shroud 11, there are cut-offportions 12 and 13 which have curved peripheries. These cut-off portions12 and 13 are exposed to the hot gas so that the thermal stress islikely to be concentrated in these areas and cause cracks 80 and 81, asshown. Therefore, these portions have to be cooled to suppress the metaltemperature as low as possible. However, these portions are so distantfrom the passage of the cooling air flowing out of air holes 17 of themoving blade 10 that they are hardly permit the cooling air.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide a structurewhich is able to suppress the metal temperature of cut-off portions orthe concentrated stress portions of a tip shroud of a moving blade thatis to be cooled through holes at the downstream stage of a gas turbineand to extend the creep lifetime of the tip shroud, by cooling thecut-off portions effectively with the cooling air.

The invention provides the following means for achieving theabove-specified object.

A gas turbine moving blade tip shroud for guiding cooling air from theroot of a moving blade into the blade to guide the cooling air, havingcooled the moving blade, so as to flow out from a plurality of air holesof the tip shroud. A guide cover enclosing and covering a portion of theair holes is mounted on the upper face of the tip shroud and is providedat its one end with an opening so that the cooling air may be guidedfrom the opening to a high stress portion in the periphery of the tipshroud.

According to the present invention, the guide cover is mounted on thehigh stress portion of the tip shroud and encloses a portion of the airholes in the upper face of the tip shroud. The guide cover has, at itsone end, an opening which is directed to feed the cooling air toward theportion that is likely to receive the influence of the hot combustiongas. This portion is cooled with the cooling air, which passes it sothat the metal temperature rise is suppressed so as to prevent cracksdue to thermal stress. In the tip shroud of the moving blade to be usedat the downstream stage of the gas turbine, the portion susceptible tobeing influenced by the hot combustion gas is located at the cut-offportions having the peripheries curved at the circumferential endportions. If these cut-off portions are opened for the upper guidecovers, thereby to effect the outflow of the cooling air, they aresuppressed in the rise of the metal temperature so that they can beprevented from cracking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-1(b) show a tip shroud of a gas turbine moving bladeaccording to one embodiment of the invention, FIG. 1(a) is a top planview, and FIG. 1(b) is a side elevation;

FIG. 2 is a sectional view taken in the direction of arrows A--A of FIG.1;

FIG. 3 is a sectional view taken in the direction of arrows B--B of FIG.1;

FIGS. 4(a)-4(c) show one cooling guide cover used in the tip shroud ofthe gas turbine according to the embodiment of the invention, FIG. 4(a)is a top plan view, FIG. 4(b) is a side elevation of a sealed portion,and FIG. 4(c) is a longitudinal side elevation;

FIGS. 5(a)-5(c) show the other cooling guide cover used in the tipshroud of the gas turbine according to the embodiment of the invention,FIG. 5(a) is a top plan view, FIG. 5(b) is a side elevation of a sealedportion, and FIG. 5(c) is a longitudinal side elevation;

FIGS. 6(a)-6(b) show a gas turbine moving blade and a tip shroud of theprior art, FIG. 6(a) is a side elevation, and FIG. 6(b) is a top planview of the tip shroud;

FIGS. 7(a)-7(b) show a prior art gas turbine moving blade, FIG. 7(a) isa longitudinal section, and FIG. 7(b) is a section taken in thedirection of arrows C--C of FIG. 7(a); and

FIGS. 8(a)-8(b) show another example of a prior art gas turbine movingblade, FIG. 8(a) is a longitudinal section, and FIG. 8(b) is a sectiontaken in the direction of arrows D--D of FIG. 8(a).

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will be specifically described withreference to the accompanying drawings.

FIG. 1 shows a tip shroud of a gas turbine moving blade according to oneembodiment of the invention. In particular, FIG. 1(a) is a top planview, and FIG. 1(b) is a side elevation. In FIG. 1, reference numeral 10designates a moving blade having a tip shroud 11. Numeral 17 designatesa plurality of air holes which extend through the tip shroud 11 andcommunicate with the holes of the moving blade 10.

Numerals 12 and 13 designate cut-off portions which are curved at theirperipheries in the two circumferential end peripheries of the tip shroud11 such that these portions are the most subjected to thermal influencescaused by hot combustion gas passing the curved portions. Numerals 14,15 and 16 designate flanges on the upper face of the tip shroud 11.These structures are identical to those of the prior art. In the presentinvention, as shown in FIG. 1(b), grooves 31 and 32 are worked or formedin the side of one end of the tip shroud 11, and grooves 33 and 34 areworked or formed in the opposite side. A cooling guide cover 21 isinserted and soldered at its two ends in the grooves 31 and 32, andanother cooling guide cover 22 is mounted in the grooves 33 and 34.

The cooling guide cover 21 covers one of the air holes 17, whichcommunicates with the holes of the moving blade 10 and is worked so asto be closed at its inner side by a member 21a and at its side face by amember 21b and opened at its outer side. On the other hand, the coolingguide cover 22 also covers two of the air holes 17 communicating withthe multi-holes of the moving blade 10 and is worked to be closed at itsinner side by a member 22a and to be opened at its outer side.

FIG. 2 is a sectional view taken in the direction of arrows A--A of FIG.1 and shows the mounted state of the cooling guide cover 21. As shown,the grooves 31 and 32 are formed in the tip shroud 11, and the coolingguide cover 21 is fitted at its end portions in those grooves to coverthe air hole 17 and is shaped so as to be closed at its inner side bythe member 21a and at its side face by the member 21b.

FIG. 3 is a sectional view taken in the direction of arrows B--B of FIG.1 and shows the state in which the other cooling guide cover 22 ismounted. As shown, the grooves 33 and 34 are formed in the confrontingfaces of the flanges 15 and 16 of the tip shroud 11, and the coolingguide cover 22 is fitted and mounted at its two ends between the grooves33 and 34 to cover the air hole 17.

FIG. 4 shows the structure of the aforementioned cooling guide cover 21.FIG. 4(a) is a top plan view, FIG. 4(b) is a side elevation of thesealed portion, and FIG. 4(c) is a longitudinal side elevation. Asshown, the cooling guide cover 21 is worked into a cover which is shapedto seal its faces to confront the tip shroud 11 with the members 21a and21b, respectively, but to open one side 21c.

FIG. 5 shows the other cooling guide cover 22. FIG. 5(a) is a top planview, FIG. 5(b) is a side elevation of the sealed portion, and FIG. 5(c)is a longitudinal side elevation. As shown, the cooling guide cover 22is worked and shaped to close the space, as formed by the flanges 15 and16 of the tip shroud 11 in conformity to the curved shape of the innerside, with the member 22a and the space, as formed by the flanges 15 and16, with a flat-shaped cover, but to open one side 22c.

According to the tip shroud of the gas turbine moving blade of theembodiment thus far described, the cooling air from the air holes 17 canbe guided to cut-off portion 12 by mounting the cooling guide cover 21on one side of the upper face of the tip shroud 11, and the cooling airfrom the air holes 17 can be guided to flow to the other cut-off portion13 by mounting the cooling guide cover 22 on the other side of the upperface of the tip shroud.

As shown in FIG. 1, more specifically, cooling air 40 from the movingblade 10 flows out of the air holes 17 to the upper face of the tipshroud 11 and further from the inside, as closed with the cooling guidecover 21, through the opening 21c and cools the surface of the cut-offportion 12 until the cooling air finally flows to the outside. On theother hand, the cooling air 40 having flown out from the air holes 17into the other cooling guide cover 22 flows to the opposite side, asclosed with the member 22a, and further flows out from the opening 22cand cools the cut-off portion 13 until the cooling air finally flows tothe outside.

The cut-off portions 12 and 13 of the tip shroud 11, which provide thepassages for the hot combustion gas so that the thermal stress isconcentrated, are exposed to the cooling air so that the temperature ofthe metal at these portions can be suppressed to a low level so as toextend the creep lifetime of the tip shroud 11.

Since the cut-off portions 12 and 13 are provided with the cooling guidecovers 21 and 22 to guide the cooling air to flow out from theiropenings, the hot combustion gas having passed the curved cut-offportions 12 and 13 of the adjoining the tip shrouds in the prior art isblocked in the invention by the cooling air so that the hot combustiongas is throttled. This further enhances the effect for those portions tosuppress the temperature rise.

What is claimed is:
 1. A gas turbine moving blade tip shroud for guidingcooling air received from a root of a moving blade, said gas turbinemoving blade tip shroud comprising:a plurality of air holes formed inthe tip shroud; a guide cover enclosing and covering a portion of saidair holes, said guide cover being mounted on an upper face of said tipshroud, wherein one end of the guide cover is open at a high stressportion in a periphery of said tip shroud so that the cooling air may beguided from said portion of said air holes covered by said guide coverto said high stress portion.
 2. A gas turbine moving blade tip shroud asclaimed in claim 1, further comprising a pair of grooves formed in theupper face of said tip shroud, wherein opposite edge portions of saidguide cover are received in said grooves, respectively.
 3. A gas turbinemoving blade tip shroud for guiding cooling air received from a rootportion of a moving blade, said gas turbine moving blade tip shroudcomprising:a plurality of air holes formed in the tip shroud; a firstguide cover enclosing and covering at least one of said air holes, saidfirst guide cover being mounted on an upper face of said tip shroud,wherein one end of said first guide cover is open at a first high stressportion in a periphery of said tip shroud so that the cooling air can beguided from said at least one air hole directly to said first highstress portion; and a second guide cover enclosing and covering at leastone of said air holes, said second guide cover being mounted on an upperface of said tip shroud, wherein one end of said second guide cover isopen at a second high stress portion in the periphery of said tip shroudso that the cooling air can be guided directly to said second highstress portion.
 4. A gas turbine moving blade tip shroud as claimed inclaim 3, wherein said first high stress portion is located at anupstream side of said tip shroud and said second high stress portion islocated at a downstream side of said tip shroud relative to a flow ofhot combustion gas.
 5. A gas turbine moving blade tip shroud as claimedin claim 3, further comprising:a first pair of grooves formed in theupper face of said tip shroud, wherein opposite edge portions of saidfirst guide cover are received in said first pair of grooves,respectively; and a second pair of grooves formed in the upper face ofsaid tip shroud, wherein opposite edge portions of said second guidecover are received in said second pair of grooves, respectively.
 6. Agas turbine moving blade tip shroud for guiding cooling air receivedfrom a root of a moving blade, said gas turbine moving blade tip shroudcomprising:a plurality of air holes formed in the tip shroud; anelongated guide cover mounted on an upper face of said tip shroud andhaving an open end and a closed end, said guide cover covering at leastone of said air holes, wherein said closed end of said guide cover islocated near said at least one air hole and said open end is located ata high stress portion in a periphery of said tip shroud, wherein saidguide cover forms a channel for guiding the cooling air from said atleast one air hole to said high stress portion.
 7. A gas turbine movingblade tip shroud as claimed in claim 6, further comprising a pair offlanges formed on the upper face of said tip shroud and a pair ofgrooves formed in said pair of flanges, respectively, wherein oppositeedge portions of said guide cover are received in said grooves,respectively.